1. Field of the Invention
The present invention relates to a process and processor for reusing a waste paint discharged from processes such as coating process of applying paint to a vehicle body.
2. Description of the Related Art Including Information Disclosed under 37 CFR 1.97 and 1.98
For instance, in a paint shop, a vehicle body is painted out by spraying coatings in a paint booth. In spraying coatings, there is some coating liquid which is not adsorbed onto the vehicle body due to spray missing (overspray). The missing spray coating enters into circulating water in a pit on the lower side of the booth, and is led to a settling (precipitation, deposit) tank together with the water. After some time period, soft cake-like masses settle and these are collected as waste paints. The waste paint is burnt up, or otherwise is dried and ground as a processed waste paint which is generally used for asphalt sheets and chipping resistant coatings.
However, the waste paint collected in the paint booth is not cured because it is not passed through a curing process. Therefore it is necessary to completely cure the waste paint to pulverize it for its reuse.
Examples of processors for drying and pulverizing the waste paint include a screw drying machine, a stirring drying machine and a rolling drying machine. Methods for processing the waste paint by using the screw drying machine, the stirring dryer and the rolling dryer are explained below.
FIG. 4 is a schematic view for explaining the screw drying machine. In the screw drying machine 100, the waste paint placed in a hopper 101 is introduced into a screw dryer 105 by a screw conveyor 102 and a belt conveyor 103, and dried in the screw dryer 105 to be pulverized, whereby the waste paint can be converted into resources.
The screw dryer 105 is provided with a cylindrical processing tank 106 into which the paint waste is introduced by the belt conveyor 103, a rotating grinding rotor 107 having plural grinding rotors 107b mounted on a rotating axis 107a which is horizontally extended in a processing tank 106, and a screw conveyor 108 disposed on the lower side of the processing tank 106.
When the waste paint is introduced into the processing tank 106, the grinding of the waste paint is started by rotation of the rotating grinding rotor 107, and simultaneously its heating is started by steam. In the process of heating of the waste paint, the waste paint is melted to form a large mass having high viscosity (e.g., heated rice cakes). In this condition, the heating promotes the vaporization of a solvent in the waste paint to dry out the waste paint.
When the waste paint is heated, the curing of a resin component in the waste paint is proceeded, and as a result the cured waste paint is ground by the rotating grinding rotor 107. The ground waste paint (i.e., resin powder) is fed as resources from the lower side of the processing tank 106 by the screw conveyor 108.
On the other hand, the water and solvent contained in the waste paint are vaporized in the processing tank 106, and the vaporized water and solvent are liquefied or condensed by a heat exchanger 109 to be discharged as condensed liquid. In this case, hydrocarbon is removed and only nontoxic gas is discharged. A reference number 109a is a vacuum pump for reducing pressure in the heat exchanger 109.
FIG. 5 is a schematic view for explaining the stirring and drying machine. In the stirring and drying machine 110 provided with a stirring dryer 115, the waste paint placed in a hopper 101 is introduced into the stirring dryer 115 by a screw conveyor 102 and a belt conveyor 103 in the same manner as the screw drying machine 100, and similarly dried in the stirring dryer 115 to be pulverized, whereby the waste paint is converted into resources.
The stirring dryer 115 is provided with a cylindrical processing tank 116 having a bottom into which the paint waste is introduced by the belt conveyor 103, a rotating grinding rotor (grinder) 117 with grinding rotors 117b mounted on a rotating axis 117a which is perpendicularly extended in the processing tank 116, and an outlet 118 disposed on the lower side of the processing tank 116.
When the waste paint is introduced into the processing tank 116, grinding of the waste paint is started by rotation of the rotating and grinding rotor 117, and simultaneously its heating is started by the steam. In the course of heating the waste paint, the waste paint is melted to form large masses having high viscosity (e.g., heated rice cakes). In this condition, the heating promotes the vaporization of a solvent in the waste paint to dry out the waste paint.
When the waste paint is heated, the curing of a resin component in the waste paint is proceeded, and as a result the cured waste paint is ground by the grinding rotor 117. The ground waste paint (i.e., resin powder) is fed as resources from the outlet 118 provided on the lower of the processing tank 116.
Water and solvent contained in the waste paint are vaporized in the processing tank 116, and the vaporized water and solvent are liquefied or condensed by a heat exchanger 109 to form condensed liquid in the same manner as the screw drying machine 100, and hydrocarbon is removed to discharge only nontoxic gas into atmosphere.
FIG. 6 is a schematic view for explaining the rolling drying machine. In the rolling drying machine 120 having a rolling dryer 121, waste paint placed in a hopper 101 is introduced into the rolling dryer 121 by a screw conveyor 102 and a belt conveyor 103 in the same manner as the screw drying machine 100, and similarly dried in the rolling dryer 121 to be pulverized, whereby the waste paint is converted into resources.
The rolling dryer 121 is provided with a box-shaped processing tank 122 into which the paint waste is introduced by the belt conveyor 103, a pair of rotating drums 123 which are horizontally disposed opposite to each other in the processing tank 122 and which rotate in the opposite direction each other, a scraper blade 124 whose edge is contact with the surface of each of the drums 123, and a screw conveyor 125 disposed on the lower side of the processing tank 122.
A large mass of waste paint, which is introduced from the upper side of a processing tank 122, is fed between a pair of rotating drums 123 opposite to each other, rolled therebetween under heating, whereby drying and grinding are started. The rolled and dried waste paint is adhered onto the surface of the rotating drums 123 to be moved by rotation of the drums, and scratched up by the scraper blade 124. The scratched waste paint is fallen from the drums 123 and fed as resources from the lower side of the processing tank 121 by the screw conveyor 125.
Water and solvent contained in the waste paint are vaporized in the processing tank 121, and the vaporized water and solvent are liquefied or condensed by a heat exchanger 109 in the same manner as the screw drying machine 100, and hydrocarbon is removed to discharge only the nontoxic gas into the atmosphere.
According to a method for processing the waste paint using the screw drying machine shown in FIG. 4, the collected waste paint is stirred under heating by the rotating grinding rotor 107 within the processing tank 106 and therefore it is gradually cured. In a beginning stage of the curing, the waste paint is increased in viscosity to become high viscous (such as in the condition of heated rice cake), and therefore resistance for rotating of the rotating grinding rotor 107 is increased and subsequently power for driving the rotor (e.g., consumed power of electric motor) is also increased. For the reason, it is required to switch the rotation number (speed) of the rotating grinding rotor 107 to a low rate and much time is taken for reduction of water content of the waste paint.
Also in the method for processing the waste paint using the stirring and drying machine shown in FIG. 5, the collected waste paint is stirred under heating by the rotating grinding rotor 117 within the processing tank 116 and therefore it is gradually cured. In the beginning stage of the curing, the waste paint is increased in viscosity to become high viscous (such as in the condition of heated rice cake), and therefore the resistance to rotation of the rotating grinding rotor 117 is increased and subsequently the power for driving the rotor (e.g., consumed power of electric motor) is also increased. For the reason, it is required to switch the speed of the rotating grinding rotor 117 to a low rate and much time is taken for reduction of the water content of the waste paint.
According to a method for processing the waste paint using a rolling and drying machine shown in FIG. 6, the collected waste paint is rolled and heated between a pair of rotating drums 123 opposite to each other to be dried. However, much time is taken for obtaining waste paint having low water content of the waste paint by the rolling and dehydrating/drying by the rotating drums 123 and therefore it is difficult to successfully perform the method.
The method for processing waste paint using the screw, stirring or rolling drying machine requires much time and cost for processing the waste paint. Hence, an efficient method for processing the waste paint is desired
As a result of many experiments, it was found that, in the drying stage of the waste paint by the stirring dryer, there are some relationships among variations of characteristics of the waste paint, that of stirring power, that of temperature of the waste paint and the water content.
The experiment was carried out as follows: 8 kg of the waste paint having 30% by weight was dried using a stirring dryer of volume of 20 L under the conditions of steam pressure of 5 kg/cm3. As a result, the drying characteristics of the waste paint are shown in FIG. 7.
The drying characteristics of the waste paint of FIG. 7 indicates the followings: In the beginning stage of the curing of the waste paint by rotating the grinding rotor and by drying by heat, value of electric current for driving the rotor is rapidly increased due to high viscosity of the waste paint, and simultaneously the content of water in the waste paint is drastically reduced whereby the waste paint is made in critical state to be destroyed. As a result, the current value is suddenly lowered because of reduction of load of the electric motor, and then the current value is approximately kept in constant while the water content is gradually reduced. Hence, it is understood that the beginning stage using the waste paint having relative high content of the water requires high power.
On the other hand, the rolling dryer rolls the waste paint between a pair of rotating drums and therefore it is difficult to sufficiently reduce the content of water after the processing by rolling. However, it has been confirmed by the experiments that the continuous rolling of the waste paint enables efficient drying (dehydration) in the beginning stage in a short time by a relative low power.
In view of the above-mentioned drying characteristics of the stirring dryer and rolling dryer, an object of the invention is to provide a process and processor for reusing waste paint (i.e., a process and processor for converting waste paint into resources) which bring about efficient processing of the waste paint.
The present invention to attain the object is provided by a process for reusing a waste paint comprising:
rolling the waste paint between a pair of heated rotating drums disposed opposite to each other for dehydrating and drying the waste paint; and
grinding the dehydrated and dried waste paint by a rotating grinding rotor of which axial is perpendicularly arranged in a processing tank for dehydrating, drying and pulverizing it.
According to the above-mentioned invention, the rough drying step includes heating and dehydrating/drying waste paint having relative high content of water by rolling it between a pair of heated rotating drums. In the rough drying by the use of the rotating drums, the rotating drums can be rotated at a constant rate, and power for dehydrating and drying the waste paint is extremely low, and further the characteristics of thermoset resin of the waste paint are destroyed.
In the main drying step, the waste paint roughly dried in the rough drying step is ground and dried by means of a rotating grinding rotor in a processing tank to convert into resources (materials). The waste paint in this main step is easily and efficiently ground at short time in a low power because the characteristics of thermoset resin of the waste paint are already destroyed in the rough drying step.
Hence, the process of the invention enables the waste paint to convert into pulverized waste paint suitable for resources in extremely less energy, whereby the reuse of the waste paint can be easily and efficiently performed. Another embodiment to attain the object is provided by a processor for reusing a waste paint comprising:
a rolling dryer comprising a pair of heatable rotating drums disposed opposite to each other for rolling the waste paint introduced therebetween to dehydrate and dry it, and
a stirring and grinding rotor for grinding the dehydrated and dried waste paint to dehydrate, dry and pulverize it; and
a processing tank provided with the grinding rotor whose axis is perpendicularly arranged in the tank. it.
According to the above-mentioned invention, by using the processor provided with the rolling dryer which heats and dehydrates/dries the waste paint having relative high content of water by rolling it between a pair of heated rotating drums, and a stirring dryer which grinds and dries the waste paint whose characteristics of thermoset resin are destroyed to convert into resources (materials), the process described above can be advantageously performed.
In the processor, the rolling dryer is preferably provided with a scraper blade in the form of plate which is arranged on each of the rotating drums in the width direction of the drum and whose edge is in contact with the surface of each of the drums to scratch up the dehydrated and dried waste paint on the drums.
In case of the use of the above-mentioned rolling dryer, the dried waste paint adhered onto the surface of the rotating drums can be easily scratched up by the scraper blade with rotating of the drums whereby the processing of the waste paint by the rolling dryer can be efficiently performed.
In the processor, the scraper blade preferably has plural cutter blades which are arranged at predetermined intervals each other along the edge of the scraper blade in the direction perpendicular to the edge.
In case of the use of the scraper blade, the plural cutter blades cut the waste paint scrapped from the surface of the rotating drums, and therefore handling when the waste paint is fed to the stirring dryer is easy, whereby the processing of the waste paint can be efficiently performed.